The effect of temperature on sorbitan surfactant monolayers

The effect of temperature on four sorbitan ester (Span 20, sorbitan monolau rate; Span 40, sorbitan monopalmitate; Span 60, sorbitan monostearate; and Span 80, sorbitan monooleate) monolayers was analyzed. The covered temperat ure range was from 22 to 42 degreesC. Surface pressure-molecular area isoth erms were measured with a Langmuir-type instrument, As the temperature was increased, the monolayers expanded more. This change can also be seen from the surface compressional modulus that was lowered as the temperature was i ncreased. Also, the collapse pressure was lowered as the temperature was in creased. (C) 2001 Academic Press.